When I was with Trek many years ago, we did hardness testing on a variety of chainrings. Stronglight were the hardest, closely followed by Campagnolo. Japanese rings (Shimano, Sugino, Sakae Ringyo) were next, and all pretty close to each other. TA were the softest.
But my experience with recent TA rings suggests that they are made from a harder alloy than they used back in the 80s, although I can offer no empirical data to support that.